Four-cycle internal combustion engines have, as their name implies, four cycles (strokes): (1) intake stroke, (2) compression stroke, (3) power stroke, and (4) exhaust stroke. A simplistic explanation of the four cycles begins with the piston at top dead center (TDC), intake stroke initiates with the opening of intake valve as the piston begins to move down the cylinder. The open intake valve permits the introduction of air and fuel into the combustion chamber. The downward movement of the piston creates a vacuum that pulls an air-fuel mixture into the cylinder. As the piston reaches bottom dead center (BDC), intake valve closes. At this point, intake and exhaust valves are closed. During the compression stroke, the piston moves up the cylinder, compressing an air-fuel mixture. As the piston reaches TDC, a spark plug ignites the mixture converting the potential energy of the air/fuel mixture into kinetic energy. During the power stroke, the pressure created by exploding air-fuel mixture forces the piston down the cylinder and the power created by the explosion is captured as mechanical energy, which turns the crankshaft as the reciprocating motion of the piston is converted into rotational motion by the crankshaft. As the piston reaches BDC, the exhaust valve opens. During the exhaust stroke, the piston moves back up the cylinder forcing the waste gases out of the combustion chamber through the open exhaust valve. At TDC, the exhaust valve closes and the four-cycle process begins again. A video at “Animated Engines—Four Stroke” visualizes the four-cycle process.
The precise control of intake valve and exhaust valve in a four-stroke engine is more complicated than as described in the commonly utilized simplistic explanation. With intake stroke, intake valve opens while the piston is moving up the cylinder and reaches a point a few degrees prior to reaching TDC position. The number of degrees dictated by the design of the camshaft is fixed. The piston continues to TDC, reverses direction, and starts back down the cylinder. The downward movement of the piston creates a vacuum that pulls an air-fuel mixture into the combustion chamber through the open intake valve port. Intake valve opens a few degrees after bottom dead center (ABDC). The number of degrees is fixed by the design of the camshaft. At this point, intake and exhaust valves are closed for the beginning of the compression stroke. During the compression stroke, a few degrees before top dead center (BTDC), the spark plug ignites the mixture. The engine control system determines when this occurs. During the power stroke, the pressure created by the exploding air-fuel mixture forces the piston down the cylinder. During the exhaust stroke, the exhaust valve opens a few degrees before bottom dead center (BBDC). The precise number of degrees when this occurs is fixed by the design of the camshaft is fixed. The piston is then forced back up the cylinder forcing the waste gases and combustion by-products out of the combustion chamber through the exhaust valve. A few degrees after top dead center (ATDC), the exhaust valve closes. At this point in the cycle both valves, intake and exhaust, are open. This is called the overlap. An example of overlap can be seen at “Engine camshaft animation (500-7000 rpm at the end).”
Most four-cycle internal combustion engines utilize a lobed camshaft that is fixed in its duration, (i.e., the number of degrees of crankshaft rotation where intake and exhaust valves are open), and timing, (i.e., the rotational position of the crankshaft in degrees BTDC/BBDC where the valves start to open and the position of crankshaft in degrees ABDC/ATDC where the valves are closed). The duration and timing dictate to a large degree the smoothness at idle and the maximum horsepower. In automobiles, a smooth idle is very desirable for occupant comfort.
Horsepower of these engines can be increased by installing superchargers and/or turbochargers. Superchargers and turbochargers add cost and complexity, leading to additional opportunity for engine failure. Both superchargers and turbochargers require a “waste gate” that regulates the internal pressure of intake system by bleeding off the pressure, thus preventing “preignition.” Waste gates direct excess pressure into the exhaust system, thus wasting energy created by turbochargers and superchargers. Pre-ignition is an event where the air/fuel mixture in the cylinder ignites before the spark plug actuates and can severely damage an engine. Pre-ignition, in its milder form, is termed “knock.” Cars with computer-controlled engines have “knock sensors,” typically a microphone tuned to listen for knock(s), which detect these pre-ignition events and signal the engine control system, which acts to reduce ignition advance. A video depicting knocking, pre-ignition and examples of damage caused by pre-ignition can be found in “Knocking and Pre-ignition.”
In U.S. Pat. No. 5,249,553, duration is determined by the cams and intake/exhaust ports. The cam duration is derived by measuring the number of degrees it is open to the combustion chamber. Intake/exhaust port duration is derived by measuring the number of degrees during which intake/exhaust cams are open. In U.S. Pat. No. 5,249,553, the cam's contribution to duration is approximately 140° while intake/exhaust port contribution is approximately 80°. The camshaft is geared to rotate half the rate as the crankshaft. To determine the duration, the two (2) angles (140° and 80°) are summed (220°) and then doubled, resulting in 440°. Engines with this degree of duration are not suitable for everyday use. A camshaft for a racing engine, COMP Cams Catalogue part #01-710-9 [37], has 322° degrees of intake duration and 330° of exhaust duration. The revolutions per minute (RPM) range for an engine equipped with this camshaft is 5000 to 7800. “Parts Details: Buick 4.1 L camshaft” depicts camshaft specifications, including duration (exhaust 194°/intake) 188°, for a typical engine, e.g. a Buick V-6. Duration can be listed two ways; one is an absolute measurement while the other is duration once the valve has lifted 1.27 mm (0.050 inch). Poppet valves are not functional until they are moved 1.27 mm (0.050 inch) off their seat, resulting in two different durations listed.
U.S. Pat. Nos. 8,210,147, 8,459,227, and 8,776,756 have extremely complicated mechanisms with many additional parts. They employ an additional crankshaft, two connecting rods, two sliding spool valves, and six pairs of sealing rings. All of these would act to limit the maximum RPM achievable as these reciprocating motions would add to existing noise and vibration created by the engine crankshaft, connecting rods, and pistons.
In U.S. Pat. No. 6,308,677, the oval-shaped cam ports restrict maximum flow. Additionally, this configuration provides only one level of horsepower and idle characteristics.
U.S. Pat. No. 6,651,605 discloses a complex valve system combined with a throttle. The camshaft rotates within a throttle shaft, which is a metal cylinder with cutouts to control flow. This configuration creates significant friction between the camshaft and throttle shaft, which increases with RPMs, and makes it difficult to regulate the throttle.
U.S. Pat. No. 7,044,097 employs a cylinder head with two rotatable camshafts. The camshafts have ports perpendicular to the axis of the camshaft. This configuration provides only one set of engine performance characteristics.
U.S. Pat. No. 6,006,714 provides an alternative to poppet valves for motor vehicles and other applications including gasoline, diesel, natural gas or other internal combustion engines. The aspiration system of the present invention operates without reciprocating valve heads and associated valve seats or other conventional seals and without any valve elements that extend into the engine cylinders.
U.S. Pat. No. 7,089,893 utilizes a valve system for a combustion engine, which possesses a fixed cylindrical valve shaft.
The aforementioned inventions suffer from a number of disadvantages, such as changing the duration and/or timing requires engine disassembly and existing camshaft(s) must be removed and replaced with camshaft(s) of different duration and/or timing and the engine reassembled; changing lobed camshaft(s) is expensive and time consuming, requiring numerous special jigs, tools, and fixtures; idle characteristics for these inventions are fixed; maximum horsepower is fixed; engines equipped with poppet valves are limited in terms of maximum RPMs and poppet valves are reciprocating mass prone to failure because as the engine RPMs rise, the reciprocating mass will overcome the resistance provided by the valve springs, resulting in contact between valve(s) and piston(s); each aforementioned invention has complicated reciprocating mechanisms that are prone to excessive wear and tend to limit engine maximum RPMs; poppet valve engines require clearances (valve lash) between the cam and the valve, but eventually clearances are reduced to zero and the valve will start to open, resulting in a loss of duration and timing; and manufacturing lobed camshafts is complicated and requires expensive, high precision equipment. In accordance with each invention, a four-cycle internal combustion engine contains camshaft(s), sleeve valves or other valve systems that is/are fixed in their duration and timing, necessitating a tradeoff between smooth idle and maximum horsepower. Moreover, the aforementioned inventions do not allow for individualized duration and timing for each cylinder.